In the recent years accidents caused by collision of vehicles with the trains occur more often than in the past, probably because of intensification of traffic both on automobile roads and on railroads.
Attempts have been made heretofore to prevents accidents on railroad crossings. U.S. Pat. No. 5,762,443 issued to Gelfand; Matthew Jun. 9, 1998 describes a history of the problem referring to the US Patents mentioned below.
Thus, Strieter, U.S. Pat. No. 1,344,776, and Siano, U.S. Pat. No. 1,661,051, disclose railroad gates which are normally stored in a pit extending across the roadway parallel to a railroad track and which are raised into an obstructing position across the roadway. These gates are solid, being made of struts, bars, rods, or other solid pieces, and as such do not yield under impact. They act as immovable objects which can cause considerable damage to vehicles which collide with them and considerable harm to the occupants of those vehicles.
Strauss, in U.S. Pat. Nos. 1,818,824 and 1,929,859, provides a flexible, net-like barrier for a railroad crossing which drops from the top of a pair of posts into position to block the roadway. Cables connected to each end of the net are wound around a drum having a return spring. Collisions with the net unwinds the cables against the return spring bias which permits the net to yield, providing a cushioning effect which lessens the damage to the car and its occupants. The drums are raised and lowered on slides keyed to one wall of posts fixed to the ground. The strength of the system may have been adequate for automobiles of the 1930s, but the sliding drums could never sustain the impact forces caused by the speeds common in today's automobiles.
Buford, in U.S. Pat. Nos. 2,189,974 and 2,219,127, shows a railroad crossing gate made of wire mesh surrounded by a seemingly solid collar. Motor-driven cables raise and lower the gate on hollow posts embedded in a foundation in the ground. Impacts are resisted progressively by means of weights on an extensible cable system having a considerable number of moving parts, mainly the pulleys which guide and support the cables and weights. The wear and tear on these moving parts make maintenance a frequent and costly occurrence.
Minert, U.S. Pat. No. 2,237,106, discloses a highway barrier comprising a flexible net whose cables are wound onto a pair of drums. An oppositely wound pair of cables compress springs in a pair of underground tubes to retard the movement of the vehicle which hits the net. Banschback, U.S. Pat. No. 2,251,699, shows a railroad crossing gate made entirely of wire cables with no solid parts. The gate deflects under impact against the restraining force of a pair of spring tubes 16 running parallel to the roadway on both sides thereof Hoover, U.S. Pat. No. 2,336,483, shows a deflectable railroad crossing barrier consisting of a net made entirely of wire cables. The net is connected at each end to a telescoping spring tube embedded in the ground parallel to the roadway. Each of these systems requires costly construction in order to embed the shock-absorbing spring tubes in the ground.
Waldecker, U.S. Pat. No. 4,824,282, shows a roadway barrier to stop terrorist intrusions into restricted spaces. A flexible net and inflatable airbags are located in a pit transverse of the roadway. When inflated the airbags raise the net, positioning it across the entire road. The ends of the net are connected to heavy-duty shock absorbers buried in concrete in the ground on both sides of the roadway. The shock absorbers include springs and/or fluids to dissipate the force of the impact while permitting deflection of the net. The cost of excavation and construction necessary to build this system may be worthwhile when limited to military bases, diplomatic compounds, or the like, but it is prohibitive when applied to the number of railroad crossings which should be protected by a restraining barrier.
Aforementioned U.S. Pat. No. 5,762,443 describes a heavy duty shock absorber system for resisting large forces as may be encountered, for example, in a restraining barrier for a railroad crossing. The system consists of two pairs of deep concrete bunkers, each pair being located on opposite sides of the railroad tracks. Each pair consists of two concrete bunkers arranged on opposite sides of the automobile road that crosses the railroad. Each bunker supports an upstanding concrete-filled steel pipe with a hydraulic, compressive shock absorber mounted on the steel pipe. Two grooves are formed in the ground on opposite sides of the railroad tracks. The grooves are parallel to the railroad tracks and contain metal nets the ends of which are attached to the retractable posts. When the train approaches the railroad crossing, the posts move upward and raise the metal net above the ground similar to a volleyball net stretched on the path of the vehicles.
A disadvantage of such a system consists in that it requires installation of four deep bunkers with four heavy ground structures for the upper ends of the posts and for post drive mechanisms. These ground structures have significant dimensions comparable with the size of the vehicles. Another disadvantage is that the mechanisms for raising the nets should be extremely powerful. This is because in the grooves can be filled with water which can be frozen and turned into ice compacted under the pressure of vehicles passing over the grooves in both directions. For the same reason the metal nets may be jammed and stuck in an upraise position thus causing a serious traffic problem.
Very often, however, collisions between trains and vehicles are caused on conventional railroad highway crossings of the type shown in FIG. I in an attempts of motorists to go around the gate arms when they are in a road-closing position. FIG. 1 is a plan view of a railroad crossing where highway 10 goes across railways 12 and 14. Reference numerals 16 and 18 designate gate arms in their road-closing positions. Each gate arm closes corresponding lanes for vehicles going in one direction. It can be seen that a motorist of a vehicle 20 can bypass the gate arm 16 going around it via the lanes for traffic in the opposite direction, e.g., along the path shown by a broken line L.
Furthermore, a disadvantage of all known systems described above is that none of them is interlocked with a visual or sound warning signal that may be activated if the barrier has failed and a vehicle has stuck on the railroad tracks.